This is a MERIT Award extension. The previous objective of this proposal was to determine the role that alpha V integrins play in tumor angiogenesis. Early work in our laboratory showed that integrin avB3 was highly upregulated on tumor associated blood vessels and that antagonists to this integrin suppressed tumor angiogenesis in animal models leading to a suppression of tumor growth. The anti-angiogenic effect of these alpha V integrin antagonists was associated with their ability to promote increased apoptosis of angiogenic endothelium in vivo. Based on these findings, several clinical trials have begun to test both antibody and small molecule alpha V integrin antagonists in late stage cancer patients. Early results indicate that agents produce little if any side effects and appear to promote disease stabilization in some patients. Over the most recent funding cycle of ths award, we have made several specific discoveries that help us gain a basic understanding of the role avB3 and avB5 play in tumor angiogenesis. For example, we identified some of the key integrin-mediated signaling events that contribute to the growth of new blood vessels. To this end, we showed that avp3 and avp5 regulate distinct pathways of angiogenesis and in so doing, differentially activate Raf kinase an important signaling intermediate leading to activation of Map Kinase in endothelial cells. We have begun to characterize the mechanism by which different angiogenic growth factors depend on coordinated integrin-mediated signals to regulate how endothelial cells survive, migrate and proliferate during tumor angiogenesis. We have established an avp3-targeted gene delivery strategy enabling us to deliver genes of interest specifically to the angiogenic endothelium in tumor bearing animals. By delivering a mutant form of Raf kinase to tumor-associated blood vessels we observed a strong pro-apoptotic, and anti-angiogenic effect resulting in the regression of pre-established primary and metastatic tumors in mice. initiated from avg3 and avp5 leading to Erk activation in tumor-associated blood vessels. We will focus on elucidating the role that alpha v integrins play in endothelial cell survival, migration and proliferation using a combination of in vitro and in vivo approaches. These studies will be facilitated by our capacity to deliver mutationally active or inactive kinases as well as interfering RNA (RNAi) to angiogenic blood vessels. Together, these studies will help clarify the role alpha V integrins play in tumor-angiogenesis and thereby help to explain how antagonist of these molecules function in cancer patients. AIMS Aim 1 Characterize the role of av83 and avB5 signaling pathways to endothelial cell migration Aim 2. Examine the mechanism of alpha V integrin-mediated cell survival during angiogenesis; Aim -. 3. Evaluate the functional significance of integrin-mediated signaling events during angiogenesis in vivo by gene delivery. Aim 4. Examine the effects of anti-angiogenic gene delivery on tumor growth in vivo.